DESCRIPTION (Applicant's Abstract): This is a request for a NIH Senior Scientist Award. A major objective during the tenure of the requested award is to advance research aimed at understanding the role that speech perception capacities play in the acquisition of language. Achievement of this aim requires (1) a careful assessment of the existing research on infant speech perception and language acquisition; (2) a deeper understanding of recent developments and theorizing in relevant areas of linguistics and psycholinguistics; (3) enhancement of skills in computer modeling of developmental change; and (4) more time in the laboratory to develop the appropriate infant testing procedures for examining crucial aspects of language acquisition. Toward the first of these requirements, the applicant has just written a book which focuses on the development of speech perception capacities and their role in language acquisition. The research undertaken to complete the book has helped to set the direction for the proposed studies. Further training in relevant areas of linguistics, and visits to laboratories of investigators at the forefront of language acquisition research, are proposed to meet the second requirement. Enhancement of skills in computer modeling will be accomplished by additional course work and training in the use of these techniques and by visits to relevant laboratories to discuss modeling of developmental change in language acquisition. The increased time available to the applicant by release from teaching and committee duties will facilitate the development of the new testing procedures and help to launch the kinds of longitudinal studies needed to explore the frontiers between speech perception capacities and language acquisition. Increased understanding of the role that speech perception capacities play in acquiring language helps to identify critical processes for the successful development of communication skills. Such information has practical relevance to those involved in the formulation of treatment programs for communication disorders.